Refining process for crude glyceride oil

ABSTRACT

COVERS AN IMPROVED PROCESS FOR REFINING A CRUDE GLYCERIDE OIL CONTAINING FREE FATTY ACID IMPURITIES WHICH COMPRISES: MIXING THE CRUDE OIL WITH AN AQUEOUS SODIUM HYDROXIDE SOLUTION TO FORM AN OIL-WATER MIXTURE; ALLOWING THE MIXTURE TO REACT UNTIL THE FREE FATTY ACID IMPURITIES ARE CONVERTED INTO A SOAP STOCK, TO FORM AN OIL-WATER-SOAP STOCK COMPOSITION; DEHYDRATING THE COMPOSITION TO PROVIDE A DEHYDRATED OIL-SOAP STOCK MIXTURE; REHYDRATING THE MIXTURE IN A PRESSURIZED ENTRIFUGE AND CENTRIFUGALLY SEPARATING THE SOAP STOCK (FOOTS) FROM THE REFINED OIL. THE PROCESS PERMITS THE SINGLE STEP REFINING OF A CRUDE GLYCERIDE OIL, WITHOUT THE NEED FOR A SEPARATE DEGUMMING STEP.

Dec. 21, 1971 M. A. MARINO ETA!- REFINI NG PROCESS FOR CRUDE GLYCERIDE OIL Filed May 29, 1969 CRUDE 01 L2 \%TO 7% FFA, J %To4% GUMS, 0.1% TQP/ PARHCULATES I"50F.TO 200F.

I50F.To200F., l/2 T012 MINUTES CAUSTIC SOLUTION! I AT LEAST 10 BAUME) I50F. TO 200F.

MIX:

WATER: PREFERABLY AT A TEMPERATURE OF AT LEAST I65F.

SPRAY DRY. I50F.TO 200E WATER AN D VOLATILES PRESSURIZED CENTRIFUGE I. AT LEAST 25 PSI DIFFERENTIAL,HEAVY PHASE I65F. TO 200 F.

SOAP STOCKI DISCHARGE REFINED OIL: LIGHT PHASE DISCHARGE FURTHER PROCESSINGZ BLEACHINQWINTERIZING,

ETC.

United States Patent 3,629,307 REFININ G PROCESS FOR CRUDE GLYCERIDE OIL Morris Anthony Marino, Westchester, Frederic John Birkhaug, La Grange, and George Edward Sadek, Oak Lawn, Ill., assignors to CPC International Inc.

Filed May 29, 1969, Ser. No. 828,926 Int. Cl. Cllb 3/06 US. Cl. 260-425 11 Claims ABSTRACT OF THE DISCLOSURE Covers an improved process for refining a crude glyceride oil containing free fatty acid impurities which comprises: mixing the crude oil with an aqueous sodium hydroxide solution to form an oil-water mixture; allowing the mixture to react until the free fatty acid impurities are converted into a soap stock, to form an oil-wate'r-soap stock composition; dehydrating the composition to provide a dehydrated oil-soap stock mixture; rehydrating the mixture in a pressurized centrifuge and centrifugally separating the soap stock (foots) from the refined oil. The process permits the single step refining of a crude glyceride oil, without the need for a separate degumming step.

This invention relates to an improved process of alkali refining a glyceride oil and more particularly to a process in which it is not necessary to degum or otherwise pretreat the glyceride oil prior to the alkali refining treatment.

Glyceride oils, and more particularly edible glyceride oils, are used as salad oils, cooking oils, margarine constituents, and the like. Corn oil, in particular, is often used in these and other food applications.

A problem which arises in the purification of glyceride oils is that crude glyceride oils tend to have high contents of such materials as free fatty acids, phosphatides (phospholipids), and particulate matter, and they are often relatively viscous. Since free fatty acids, phosphatides and particula'te matter are undesirable in many edible products, crude glyceride oils are refined to remove these undesirable materials.

Before alkali refining can be efficiently carried out with crude glyceride oils which have a high phosphatide content, the crude oils must be degummed. Degumming is usually accomplished by treating the glyceride oil with water alone or with water containing a small amount of a degumming agent such as, for example, acetic anhydride. After degumming, the degummed, crude glyceride oil is much lower in free fatty acids, phosphatides and particulate matter. It also generally has a much lower viscosity. The process of degumming a crude glyceride oil, of course, increases the cost of processing the oil.

After an oil has been degummed, it can be alkali refined to improve its quality further. The phosphatides are surface active agents (lecithin and the like) and favor the formation of oil-soap stock emulsions during alkali refining. They have the effect of solubilizing the glyceride oil in the soap stock. Thus, in conventional alkali refining processes, neutral oil losses in soap stock are much higher if the phosphatides are not first removed from the oil stock by degumming.

An alternative degumming process makes use of two successive alkali refining steps. The first reduces the amount of free fatty acids, phosphatides, and particulate matter. The second step further reduces the amounts of these materials to acceptable levels. This two-step process also increases glyceride oil processing costs.

A glyceride oil, particularly an edible glyceride oil, is conventionally refined by treating it with an aqueous solution of sodium hydroxide or sodium carbonate. The alkali ice treatment improves the color of the oil. It precipitates the phosphatides, neutralizes any remaining free fatty acids by forming soaps, and entraps the particulate matter in the soaps.

Alkali refining is usually only one of several steps that are designed to place the oil in a form that is acceptable to the consumer. Other treatment such as bleaching, hydrogenating, Winterizing and deodorizing are usually employed for improving quality.

The alkali refining step tends to be practiced to disadvantage when the glyceride oil contains free fatty acids at higher levels. Larger amounts of soap are formed and are accompanied by serious oil losses, because the neutral oils are entrained or occluded in the soap. This is especially true when the glyceride oil contains surface active emulsifying agents such as phosphatides. In general, the oil loss, during the refining of such oils, is on the same order of magnitude as the amount of free fatty acids originally present in the glyceride oil.

An improved process whereby a viscous glyceride oil containing gummy material and particulate matter can be alkali refined in a single continuous process, with a lower refining loss due to saponification and entrapment of neutral oil in the separated soap stock, would be highly desirable.

In view of the above, it is an object of this invention to provide improved methods for alkali refining glyceride oils and particularly oils that have not been degummed.

A further object of the invention is to provide an improved process for refining a gummy glyceride oil whereby lower refining losses due to saponification and entrapment of neutral oil in the separated soap stock occur.

A still further object of the invention is to provide an improved process for alkali refining a viscous glyceride oil that contains substantial quantities of free fatty acids, gummy material and particulate matter.

A specific object of the invention is to develop an improved process of alkali refining a viscous corn oil which contains substantial quantities of free fatty acids, gummy material and particulate matter.

Other objects of the invention will be apparent hereinafter from the description that follows and from the appended claims.

GENERAL DESCRIPTION OF THE INVENTION Broadly speaking, the invention in one embodiment thereof is a process of refining a glyceride oil that contains free fatty acids as impurities, which comprises mixing an aqueous sodium hydroxide solution with the oil to form a mixture; allowing the mixture to react until the free fatty acids are converted into a soap stock phase, to form an oilwater-soap stock composition; dehydrating the composition to form a dehydrated oil-soap stock mixture; conveying' the dehydrated mixture into a pressurized centrifuge, and therein simultaneously rehydrating and centrifugally separating the soap stock from the refined oil. FIG. 1 is a flow diagram illustrating the process.

This process is applicable to a viscous glyceride oil which contains gummy materials such as phosphatides, dissolved protein fragments, and, as well, other particulate matter such as, for example, cellulose, starch, inorganic insolubles, and the like. The process, is, of course, also applicable to a glyceride oil which does not contain these impurities. But it is most advantageously applied to a glyceride oil containing these naturally-occurring materials, since the process of the present invention removes these materials along with the free fatty acids, with a minimal loss of glyceride oil. This is surprising in View of the fact that phosphatides are surface active agents that ordinarily solubilize glyceride oil in soap stock, and increase oil losses.

The preferred sodium hydroxide solution for use in the practice of this invention has a concentration of at least Baum. This reduces the amount of water which must be removed in the dehydration step. Preferably, the concentration of the sodium hydroxide solution is within the range from about 10 Baum to about 32 Baum.

The total amount of sodium hydroxide added to the glyceride oil is preferably not more than about 0.3% more than that necessary to neutralize the free fatty acids present. Most preferably, the excess of sodium hydroxide falls within the range from about 0.1% to about 0.3% above theoretical. The use of this amount of sodium hydroxide minimizes saponification of the glyceride oil, while ensuring neutralization of the free fatty acids.

The sodium hydroxide solution is mixed with the crude glyceride oil at a temperature preferably falling within the range from about 150 F. to about 200 F. The mixing is preferably continued for a time from about /2 minute to about 12 minutes and more preferably, from about 1 minute to about 3 minutes.

The mixing is preferably accomplished by flowing together streams of sodium hydroxide solution and glyceride oil in a pipe containing bafiles and a mechanical agitator. As the mixture flows through the pipe the bafiles and the agitator insure thorough mixing. The total residence time and temperature in the pipe are preferably those mentioned above. This allows sufiicient time in the preferred temperature range, for the sodium hydroxide to react with the free fatty acids.

Preferably, the resulting oil-water-soap stock composition is then dehydrated by vacuum drying. Typically, the vacuum drying is done by spraying the composition continuously into a chamber that is continuously evacuated. In the vacuum chamber the water and volatile gases are removed as vapors, and the dehydrated oil-soap stock mixture, which is much less volatile than the water, collects at the lower end of the chamber, and is pumped out. For efiicient operation of the vacuum drying operation, it has been found that the temperature of the chamber and its contents should be maintained within the range from about 150 F. to about 200 F., so that the vapor pressure of the water is high enough for eflicient water removal.

For efficient operation, preferably the dehydrated oilsoap stock mixture should contain no more than about 3.0% by weight of water.

After dehydration, the oil-soap stock mixture preferably is transported into a pressurized centrifuge, where it is rehydrated and centrifuged simultaneously. The rehydrating agent, preferably water, is generally heated to least about 165 F., prior to the rehydration. Other suitable rehydration agents include water and water solutions of neutral or weakly acidic or basic materials which do not react with the oil. Examples of such materials include salts, for example sodium chloride, sodium sulfate, sodium silicate, potassium acetate, and the like and weak organic acids such as citric acid.

The, soap stock is centrifugally separated from the refined oil at a temperature within the range from about 165 F. to about 200 F. More preferably, the centrifuge is operated at a temperature that falls within the range from about 185 F. to about 200 F. In the trade, the resulting soa stock, which consists of saponified free fatty acids, precipitated phosphatides, and particulate matter, is referred to as foots.

It is essential to the practice of this invention, when refining a glyceride oil which has not been degummed or subjected to a prior alkali refining step, and which contains significant quantities of free fatty acids, phosphatides, and particulate matter, that the pressurized centrifuge be op erated with a pressure differential of at least p.s.i. At lower pressure differentials, the dehydrated oil-soap stock mixture is too viscous for eflicient separation.

It is highly preferable that the rehydration of the oil-soap stock supply be performed within the centrifuge, and the soap stock be centrifugally separated from the refined oil essentially immediately upon rehydration. Most preferably, the rehydrating agent is added, within the centrifuge, to the soap stock (heavy) phase of the oil-soap stock supply.

Generally, it is preferable to operate the pressurized centrifuge at a pressure differential which falls within the range from about 25 p.s.i. to about 75 p.s.i. This is preferably accomplished by operating the pressurized centrifuge with a discharge pressure of the refined oil (light phase) which falls within the range from about 25 p.s.i.g. to about p.s.i.g. and an inlet pressure which falls within the range from about 75 p.s.i.g. to about p.s.i.g. Most preferably, the discharge pressure is controlled so as to fall within the range from about 40 p.s.i.g. to about 70 p.s.i.g. and the inlet pressure is adjusted so as to fall within the range from about 90 p.s.i.g. to about 110 p.s.i.g. The discharge pressure of the foots (heavy phase) is at atmospheric pressure.

The inlet pressure to the pressure centrifuge is generally controlled by adjusting a pumping system. The discharge pressure is generally controlled by adjusting a discharge valve on the refined oil line. The details of the valving arrangement are unimportant so long as an adequate flow rate and discharge pressure can be obtained. Commercially available pressure centrifuges are made by the De Laval Separator Company, New York, N.Y., for example, and Work well in the above described centrifugal separation process.

It is highly preferred that the rehydrating and centrifugal separating be carried out continuously.

The preferred glyceride oil for use in the practice of this invention is a viscous non-degummed (crude) corn oil. A crude corn oil, prior to refining, generally contains an amount of free fatty acid falling within the range from about 1% to about 7%, an amount of gummy material (phosphatides, dissolved protein, etc.) falling within the range from about 1% to about 4%, an an amount of particulate matter falling within the range from about 0.1% to about 1.0% all of the precentage figures being by weight based on the total weight of the crude corn oil.

The following example illustrates the refining of a typical crude corn oil having a high viscosity and a high fatty acid content, by the method of this invention. The example is meant to be illustrative and the invention, of course, is not to be limited thereto. All parts and percentages are by weight unless expressly stated to be otherwise.

EXAMPLE Crude non-degummed corn oil (150,000 lbs.) was refined in a continuous process. The process was as follows:

The oil and a 15 Baum sodium hydroxide solution were each preheated to F. and flowed together in a bafiied pipe equipped with a mechanical agitator and then through the pipe. The pipe was maintained at 180 F. The battles and the agitator in the pipe insured good mixing of the oil and the caustic. A 0.2% excess of sodium hydroxide was maintained over that amount necessary to saponify the free fatty acids. The average residence time for the mixture in the pipe was about 2 minutes.

The crude oil-alkali mixture, after passage through the baffled pipe, was continuously spray dried under vacuum. The entire spray drier was maintained at a temperature of approximately F. The temperature was controlled by passing steam through sealed coils contained within the spray drier. A pressure of between about 24 inches and 28 inches of mercury was maintained within the spray drier.

The dehydrated, spray-dried mixture was delivered to a pressurized centrifuge. The discharge pressure (light phase) of the pressurized centrifuge was periodically adjusted for efficient separation, and was maintained within the range from about 40 p.s.i.g. to about 70 p.s.i.g. The inlet pressure to the centrifuge was adjusted at and maintained within the range from about 90 p.s.i.g. to about 110 p.s.i.g., so as to provide a pressure dilferential across the centrifuge of at least 25 p.s.i.

Water, at a temperature of about 200 F., was continuously injected into the mixture in the centrifuge. The foots or soap stock discharged continuously from the heavy phase discharge of the centrifuge and refined corn oil was taken off from the light phase discharge. Processing of the entire 150,000 lbs. of oil required about 10 hours.

During the refining procedure, 4 sampling operations were performed. Each sampling operation consisted of removing a series of 5 samples, one sample each of crude corn oil, dehydrated mixture, crude oil-alkali mixture, refined corn oil, and soap stock. Each of the 4 crude corn oil samples was analyzed to determine its free fatty acid content. Each of the 4 dehydrated mixtures was analyzed to determine its water content.

Each of the 4 crude oil-alkali mixtures refined oil, and soap stock samples was analyzed to determine its sodium content. The percent yield of refined corn oil based on total crude oil, was then calculated by the sodium balance method as described by L. S. Crauer and F. E. Sullivan, J. Am. Oil Chemists Soc., 38, 172 (1961).

The same crude corn oil was processed in essentially the same manner, but without dehydration, for comparative purposes.

The data for the processings of the crude oil are summarized in Table I.

TABLE I Free fatty Percent mois- Percent of acid content ture in the soap stock Yield of in the crude dehydrated thap was refined Sample corn oil mixture neutral oil corn oi The data indicate that when the moisture content of the crude corn oil is kept below about 3.0% in the dehydrated mixture, significantly higher yields of refined corn oil will be obtained and significantly less oil will be entrapped and lost in the soap stock, than is the case when essentially the same corn oil is refined without a dehydration step. The data further indicate that the process may be carried out successfully on a large commercial scale, for which the yield improvement is of substantial significance.

While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modification, and this application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth, and as fall within the scope of the invention.

That which is claimed is:

1. In a process for refining a crude glyceride oil having a free fatty acids content of from about 1% to about 7% by weight and a gummy material content of from about 1% to about 4% by weight by reacting an aqueous sodium hydroxide solution with said crude glyceride oil to obtain an oil-water-soa-p stock composition the improvement comprising:

dehydrating the composition to provide a dehydrated oil-soap stock having a Water content of no more than 3.0% by weight based on the total weight of the oil-soap stock supply; and

simultaneously rehydrating the oil-soap stock and centrifugally separating the oil from the soap stock in a pressurized centrifuge. 2. A process as in claim 1 wherein said dehydrating is accomplished by spray drying under vacuum.

3. A process as in claim 2 wherein said spray drying is performed at a temperature falling within the range from about 150 F. to about 200 F.

4. A process in accordance with claim 1 wherein the pressurized centrifuge operates with a pressure differential of at least about 25 p.s.i.

5. A process as in claim 4 wherein said pressure differential falls within the range from about 25 p.s.i. to about p.s.i.

6. A process as in claim 5 wherein said pressurized centrifuge has a light phase discharge and an inlet and operates with a discharge pressure at the light phase discharge which falls Within the range from about 25 p.s.ig. to about p.s.i.g. and with an inlet pressure which falls within the range from about 75 p.s.i.g. to about 150 p.s.i.g.

7. A process as in claim 6 wherein said discharge pressure falls within the range from about 40 p.s.i.g. to about 70 p.s.i.g. and said inlet pressure falls within the range from about 90 p.s.ig. to about p.s.i.g.

8. A process as in claim 1 wherein said rehydrating and centrifugal separating are carried out continuously. 9. A process as in claim 1 wherein said crude glyceride oil is a crude corn oil.

10. A process as in claim 9 wherein said crude corn oil, prior to refining contains an amount of free fatty acids falling within the range from about 1% to about 7%, an amount of gummy material falling within the range from about 1% to about 4% and an amount of particulate matter falling within the range from about 0.1% to about 1%, said percent figures being weight percent based on total weight of the crude corn oil.

11. In the process of claim 1 for refining a crude glyceride oil having a free fatty acids content of from about 1% to about 7% by weight, and a gummy material content of from about 1% to about 4% by weight by reacting an aqueous sodium hydroxide solution having a concentration within the range from about 10 Baum to about 32 Baum, with said glyceride oil, to obtain an oil-water-soap stock composition the improvement comprising:

dehydrating the composition by spray drying under vacuum at a temperature falling within the range from about F. to about 200 F. to provide a dehydrated oil-soap stock having a water content of no more than 3.0% by weight based on the total weight of the oil-soap stock supply; and

simultaneously rehydrating the oil-soap stock by adding water and centrifugally separating the oil from the soap stock in a pressurized centrifuge.

References Cited UNITED STATES PATENTS 2,683,155 7/1954 Dron 260-425 2,733,253 1/1956 Milbers et al. 260425 2,752,378 6/1956 Julian et al. 260-425 LEWIS GOTIS, Primary Examiner E. G. LOVE, Assistant Examiner 

